[英]Callback function in C does not printf
I'm trying out callback functions in C, and I'm not sure why, but for some reason printf does not work in the callback function.我正在尝试 C 中的回调函数,但我不确定为什么,但出于某种原因 printf 在回调函数中不起作用。 For example:
例如:
#include <stdio.h>
void call_this_method()
{
printf("call_this_method called\n");
}
void callback(void (*method))
{
printf("callback called\n");
(void) method;
}
int main(int argc, const char * argv[])
{
callback(call_this_method);
}
if I try to run this, only "callback called" gets printed out in the console;如果我尝试运行它,只有“回调调用”会在控制台中打印出来; "call_this_method called" does not get printed out.
“call_this_method called”不会被打印出来。 Why is that?
这是为什么?
First of all void (*method)
is a plain pointer to anything .首先
void (*method)
是一个指向任何东西的普通指针。 It's equal to void *method
.它等于
void *method
。 You should declare it as a pointer to a function void (*method)(void)
.您应该将其声明为指向函数
void (*method)(void)
的指针。
Secondly, (void) method
doesn't call anything.其次,
(void) method
不调用任何东西。 It just evaluates method
as a value on its own, and the discards that value (due to the cast).它只是将
method
评估为自己的值,然后丢弃该值(由于强制转换)。 With the above fix you call it like any other function:通过上述修复,您可以像调用任何其他函数一样调用它:
method();
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